Filter cakes are normally removed from rotary filters by means of polypropylene scrapers or VA knives immediately behind the deflecting roller. Scraper devices of this kind for precoat filters (filters with auxiliary middle layer) are described in German Offenlegungsschrift 2,059,137. The scrapers used in these devices are normally fixed in position by reciprocating scrapers are disclosed in German Offenlegungsschrift 3,243,683. Scrapers which are pressed against the belt filter by pneumatic/hydraulic means and automatically reposition themselves are also known in the art (DE 3,243,683).
These scrapers or knives have the serious disadvantage that they frequently damage the belt when they scrape off the filter cake adhering to the belt. This is partly due to the fact that most of these filters have a very wide belt (e.g. &gt;3 m) so that the belt can no longer be kept flat and is to some extent irregular over its width due to imperfections in the manufacturing process and partly due to the fact that the filter cake is not completely scraped off but rolls up and then causes trouble or damage to the belt.
The problem therefore exists of providing a stripping device for rotary filters with belt which would avoid damage to the belt.